matching dimensions.
</programlisting>
 </para>

 <para>
  The <literal>ARRAY</literal> constructor syntax can also be used:
<programlisting>
INSERT INTO sal_emp
    VALUES ('Bill',
    ARRAY[10000, 10000, 10000, 10000],
    ARRAY[['meeting', 'lunch'], ['training', 'presentation']]);

INSERT INTO sal_emp
    VALUES ('Carol',
    ARRAY[20000, 25000, 25000, 25000],
    ARRAY[['breakfast', 'consulting'], ['meeting', 'lunch']]);
</programlisting>
  Notice that the array elements are ordinary SQL constants or
  expressions; for instance, string literals are single quoted, instead of
  double quoted as they would be in an array literal.  The <literal>ARRAY</literal>
  constructor syntax is discussed in more detail in
  <xref linkend="sql-syntax-array-constructors"/>.
 </para>
 </sect2>

 <sect2 id="arrays-accessing">
  <title>Accessing Arrays</title>

  <indexterm>
   <primary>array</primary>
   <secondary>accessing</secondary>
  </indexterm>

 <para>
  Now, we can run some queries on the table.
  First, we show how to access a single element of an array.
  This query retrieves the names of the employees whose pay changed in
  the second quarter:

<programlisting>
SELECT name FROM sal_emp WHERE pay_by_quarter[1] &lt;&gt; pay_by_quarter[2];

 name
-------
 Carol
(1 row)
</programlisting>

  The array subscript numbers are written within square brackets.
  By default <productname>PostgreSQL</productname> uses a
  one-based numbering convention for arrays, that is,
  an array of <replaceable>n</replaceable> elements starts with <literal>array[1]</literal> and
  ends with <literal>array[<replaceable>n</replaceable>]</literal>.
 </para>

 <para>
  This query retrieves the third quarter pay of all employees:

<programlisting>
SELECT pay_by_quarter[3] FROM sal_emp;

 pay_by_quarter
----------------
          10000
          25000
(2 rows)
</programlisting>
 </para>

 <para>
  We can also access arbitrary rectangular slices of an array, or
  subarrays.  An array slice is denoted by writing
  <literal><replaceable>lower-bound</replaceable>:<replaceable>upper-bound</replaceable></literal>
  for one or more array dimensions.  For example, this query retrieves the first
  item on Bill's schedule for the first two days of the week:

<programlisting>
SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';

        schedule
------------------------
 {{meeting},{training}}
(1 row)
</programlisting>

  If any dimension is written as a slice, i.e., contains a colon, then all
  dimensions are treated as slices.  Any dimension that has only a single
  number (no colon) is treated as being from 1
  to the number specified.  For example, <literal>[2]</literal> is treated as
  <literal>[1:2]</literal>, as in this example:

<programlisting>
SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';

                 schedule
-------------------------------------------
 {{meeting,lunch},{training,presentation}}
(1 row)
</programlisting>

  To avoid confusion with the non-slice case, it's best to use slice syntax
  for all dimensions, e.g., <literal>[1:2][1:1]</literal>, not <literal>[2][1:1]</literal>.
 </para>

 <para>
  It is possible to omit the <replaceable>lower-bound</replaceable> and/or
  <replaceable>upper-bound</replaceable> of a slice specifier; the missing
  bound is replaced by the lower or upper limit of the array's subscripts.
  For example:

<programlisting>
SELECT schedule[:2][2:] FROM sal_emp WHERE name = 'Bill';

        schedule
------------------------
 {{lunch},{presentation}}
(1 row)

SELECT schedule[:][1:1] FROM sal_emp WHERE name = 'Bill';

        schedule
------------------------
 {{meeting},{training}}
(1 row)
</programlisting>
 </para>

 <para>
  An array subscript expression will return null if either the array itself or
  any of the subscript expressions are null.  Also, null is returned if a
  subscript is outside the array bounds (this case does not raise an error).
  For example, if <literal>schedule</literal>
  currently